Background
There is a class of audio speakers, commonly used in earphones and handsets, that have relatively poor performance at low frequencies (e.g., <800 Hz). To improve the performance of such speakers, psychoacoustic bass enhancement (PBE) has been used. Certain PBE techniques are known, and generally, these methods are based on the residue pitch theory to generate mid-frequency harmonics in lieu of low-frequency components. These harmonics cause a residue pitch phenomenon when heard by the listener, which creates the illusion that the missing low-frequency components do exist. Thus, with PBE, the listener perceives low-frequency components that are not actually reproduced because they are below the frequency levels that the speaker can reproduce. This auditory trick works because of the nature of the human auditory system.
It is known to combine PBE techniques with active noise cancellation (ANC) in headsets to improve perceived bass reproduction and low-frequency noise attenuation. An example of this combination is described in the article “Integration of Virtual Bass Reproduction in Active Noise Control Headsets,” by Woon-Seng Gan; Kuo, S. M., Signal Processing, 2004. Proceedings. ICSP '04. ANC is a technique to perform noise suppression through the production of acoustic waves equal in amplitude, but 180° out of phase relative to the target noise being suppressed. ANC is often used for near-end noise cancellation applications. This generated anti-noise cancels out the background noise through destructive interference.
Generally, it can be problematic to perform ANC with small speakers, such as headset speakers, using known ANC techniques because ANC typically relies on bulky audio speakers with good low frequency response, which are not useable with earphone headsets and mobile handsets. ANC performance is highly affected by acoustic components, especially the low-frequency response characteristics of the speaker. Some known handset speakers lack adequate low-frequency response due to the size limit of the speaker. This results in suboptimal near-end noise cancellation when using ANC. Moreover, known techniques of combining PBE and ANC in headset speakers, such as those described in Woon-Seng Gan et al., do not fully integrate the operation of the PBE and ANC methods, which may also result in suboptimal performance. For example, in Woon-Seng Gan's disclosed system, feedback from the ANC process is not provided to the PBE process so as to optimize overall system performance.